The construction of a brain probe assembly to be employed in brain research is quite challenging from both a structural and an electrical standpoint.
Structurally, probes must not fray or in any way come apart when pushed through the dura, a tough membrane covering the brain, and other brain tissue. Probe should have enough strength and rigidity to broach the dura without the need for assistance by, for example, a guide tube or an initial incision.
Moreover, probes must not break, running the risk of leaving a fragment in the brain. Also, they must not cause undue damage to tissue at the sensing site. Inevitably, the tissue separating the sensing site from the brain exterior will suffer some damage as a probe is pushed to its destination. A small cross-section probe, however, may cause less damage as it is pushed to its destination. It is best to avoid having a sharp tip or any sharp edges, however, as this could cause blood vessels to be severed during the insertion process.
Electrically, one should note that the electric field signals in the brain, which the probe is designed to detect, are typically of the order of 100 to 500 μvolts. The low amplitude of these signals makes it necessary to amplify them as physically close as possible to their source. In fact, the signals involved are so minute that variations in circuit geometry could well affect significantly the detection processing of the signals. It is also highly desirable to minimize cross-talk between any two signals.
Additionally, it is generally advantageous for a brain probe to become flexible after being inserted so that the motion of the brain within the brain pan is not resisted by the probe. In the worst case this could cause tissue tearing. To insert a brain probe, however, it is better for the probe to be in a rigid state. Given the tight geometries allowable for brain probe design, these requirements are difficult to meet simultaneously.